Bromodomain And Extra-Terminal (BET) proteins regulate metabolic and redox function in COPD airway smooth muscle cells

Background: Airway smooth muscle (ASM) thickening in COPD is caused by ASM cell (ASMC) hyperplasia and hypertrophy. Transforming growth factor (TGF)-β and reactive oxygen species (ROS), due to NADPH oxidase and mitochondrial activity, promote ASMC hyperplasia. The transcriptional regulators Bromodomain and Extra-Terminal (BET) proteins drive proliferative and inhibit antioxidant gene transcription in ASMCs. Aims u0026 Objectives: Determine the role of BET proteins in the oxidant-antioxidant balance and mitochondrial activity of COPD ASMCs. Methods: ASMCs were cultured from resected airways of COPD patients (n=7). BET proteins were inhibited using the compound JQ1+ in the absence or presence of TGF-β (1ng/ml) and FBS (2.5%; proliferative conditions). mRNA was measured by real-time PCR, mitochondrial membrane potential (ΔΨm) by JC-1 staining, and cytoplasmic and mitochondrial ROS by dicholofluorescein diacetate (DCF-DA) and MitoSOX staining, respectively. Results: JQ1+ (300nM) reduced NADPH oxidase 4 mRNA (Baseline: by ~90%; TGF-β/FBS: by ~90%) and cytoplasmic ROS (Baseline: ~30%; TGF-β/FBS: ~30%). JQ1+ increased the mRNA of the antioxidant enzymes MnSOD (Baseline: by ~1.5-fold; TGF-β/FBS: by ~2-fold) and haem oxygenase (Baseline: ~4.5-fold; TGF-β/FBS: ~2-fold). JQ1+ reduced the mRNA expression of the mitochondrial biogenesis activators PPAR-γ co-activator (PGC)-1α (Baseline: by ~90%; TGF-β/FBS: by ~75%) and PGC-1β (Baseline: ~60%; TGF-β/FBS: ~85%). Also, JQ1+ attenuated ΔΨm by ~20% and mitochondrial ROS by ~30% at baseline, but not under TGF-β/FBS stimulation. Conclusion: BET proteins drive oxidant-antioxidant imbalance and mitochondrial biogenesis in COPD ASMCs.